Patterning thin film layers for electroluminescent displays

ABSTRACT

The invention relates to a laser ablation method for patterning thin film layers for thick dielectric electroluminescent displays without substantial ablation of or damage to any other layers. Typically, the thin film layers are phosphor layers. The laser ablation method for patterning a thin film phosphor layer of a thick dielectric electroluminescent display comprises selecting a wavelength of laser radiation, a laser pulse length, a laser energy density and a sufficient number of laser pulses to pattern the thin film phosphor layer without substantial ablation of or damage to other layers, whereby the wavelength of laser radiation is such that the laser radiation is substantially absorbed by the thin film phosphor layer with minimal absorption by other layers, the laser pulse length is sufficiently short that during the duration of the laser pulse there is minimal heat flow from the thin film phosphor layer to other layers, and the laser energy density and the sufficient number of laser pulses is sufficiently high that energy is deposited in the thin film phosphor layer, whereby the entire thickness of at least a portion of the thin film phosphor layer is ablated.

FIELD OF THE INVENTION

[0001] The present invention relates to a laser ablation method forpatterning thin film layers for thick dielectric electroluminescentdisplays. More particularly, the invention relates to a laser ablationmethod for patterning thin film phosphor layers without substantialablation of or damage to any other layers.

BACKGROUND OF THE INVENTION

[0002] Thick film dielectric electroluminescent displays (TDEL) providea great advance in flat panel display technology. TDEL displays comprisea basic structure of, in sequence, a substrate, an electricallyconductive film layer to form the lower electrode, a thick dielectricfilm layer, a phosphor film deposited on the thick film layer, and anoptically transparent but electrically conductive film to form the upperelectrode in the structure.

[0003] Various aspects of manufacturing TDEL displays are described inApplicant's co-pending U.S. patent application Ser. No. 09/747,315 filedDec. 22, 2000; Ser. No. 09/761,971 filed Jan. 17, 2001; Ser. No.09/867,080 filed May 29, 2001; Ser. No. 09/867,806 filed May 30, 2001and Ser. No. 09/880,410 filed Jun. 13, 2001 as well as in Applicant'sU.S. Pat. No. 5,432,015 and International Patent ApplicationsPCT/CA01/01234 and PCT/CA00/00561. The disclosure of theseaforementioned applications and issued patent are hereby incorporated byreference in their entirety into the present disclosure.

[0004] TDEL displays provide for several advantages over other types offlat panel displays including plasma displays (PDP), liquid crystaldisplays (LCD), thin film electroluminescent displays (TFEL), fieldemission displays (FED) and organic electroluminescent devices (OLED).For example, TDEL displays provide greater luminescence and greaterresistance to dielectric breakdown as well as reduced operating voltage,as compared to other types of flat panel displays, such as TFELdisplays. This is primarily due to the high dielectric constant of thethick film dielectric materials used in TDEL displays which facilitatesthe use of thick layers while still facilitating an acceptably lowdisplay operating voltage. The thick film dielectric structure, whendeposited on a ceramic or other heat resistant substrate, may withstandhigher processing temperatures than TFEL devices, which are typicallyfabricated on glass substrates. This increased temperature tolerancefacilitates annealing of subsequently deposited phosphor films toimprove their luminosity and stability.

[0005] Unfortunately, thick film electroluminescent displays have notachieved the phosphor luminescence and colour needed to be fullycompetitive with cathode ray tube (CRT) displays, particularly withrecent trends in CRT specifications to higher luminescence and highercolour. Some improvement has been realized by increasing the operatingvoltage of the displays, but this increases the power consumption anddecreases the reliability of the displays.

[0006] Further improvement in the performance of thick dielectricelectroluminescent displays was realized through improved phosphorperformance. For example, it is disclosed in Applicant's co-pending U.S.patent application Ser. No. 09/798,203 filed Mar. 2, 2001 (thedisclosure of which is herein incorporated by reference in itsentirety), that an europium activated alkaline earth containing sulfideselected from the group consisting of thioaluminates, thiooxyaluminates,thiogallates, thiooxygallates, thioindates, thiooxyindates and mixturesthereof, can be employed to provide a high luminescent blue phosphorand, thus, improve phosphor performance.

[0007] In another example, improved phosphor performance was achieved,in part, by reducing phosphor damage as a result of patterning phosphorfilms, such as the blue phosphors mentioned above, before they are fullyformed and stabilized. For instance, a photolithographic process isdescribed in Applicant's co-pending International Patent ApplicationPCT/CA00/00561, (the disclosure of which is hereby incorporated byreference). A patterned phosphor film is fabricated by first depositinga uniform phosphor layer, using electron beam deposition, thenpatterning the phosphor film by applying a photoresist. The photoresistis exposed to a selected pattern of light using a suitable exposure maskand then selected portions of the phosphor film are etched away using asuitable etchant in order to form the required pattern. The patterningis done prior to heat treatment, when the phosphor is in a more reactiveand, hence, etchable state. The problem, however, with using such amethod is that the deposited patterned phosphor film is susceptable toreacting with the etchant and other chemicals used in thephotolithographic process, which causes a reduction in the fullyprocessed phosphor performance and stability. To eliminate this type ofdegradation, another process was used whereby the phosphor film isdeposited using a shadow mask such that patterning is achieved duringdeposition of the phosphor film rather than after the phosphor film isdeposited. This method, however, is generally not applicable tohigh-resolution displays whereby the required spatial definition of thepatterned film exceeds that which can be achieved using shadow masks.

[0008] Other techniques to patterning films have been described in U.S.Pat. Nos. 4,970,366 and 4,970,369. These patents are directed to laserpatterning of transparent electrically conductive layers in displayssuch as liquid crystal displays.

[0009] It is therefore desirable to improve the performance of thickdielectric electroluminescent displays, particularly the luminescenceand energy efficiency of these displays, by offering a process forpatterning thin films in thick dielectric electroluminescent displayswhich overcome the limitations of the prior art.

SUMMARY OF THE INVENTION

[0010] The present invention relates to a laser ablation method forpatterning thin film layers for thick film dielectric electroluminescentdisplays.

[0011] According to an aspect of the invention, there is provided alaser ablation method for patterning a thin film phosphor layer of athick film dielectric electroluminescent display having other layers,the method comprising selecting a wavelength of laser radiation, a laserpulse length, a laser energy density and a sufficient number of laserpulses to pattern the thin film phosphor layer without substantialablation of or damage to other layers, whereby the wavelength of laserradiation is such that the laser radiation is substantially absorbed bythe thin film phosphor layer with minimal absorption by other layers,the laser pulse length is sufficiently short that during the duration ofthe laser pulse there is minimal heat flow from the thin film phosphorlayer to other layers, and the laser energy density and the sufficientnumber of laser pulses is sufficiently high that energy is deposited inthe thin film phosphor layer, whereby the entire thickness of at least aportion of the thin film phosphor layer is ablated.

[0012] According to another aspect of the present invention is a laserablation method for patterning a rare earth activated alkaline earthsulfide phosphor film layer within a thick film dielectricelectroluminescent display comprising other layers, the methodcomprising:

[0013] providing a wavelength of laser radiation, a laser pulse length,a laser energy density and a sufficient number of laser pulses to saidphosphor layer to effect patterning of said phosphor layer withoutsubstantial ablation of, or damage to other layers,

[0014] wherein said wavelength is substantially absorbed by saidphosphor layer and there is minimal heat flow from said phosphor layerto other layers, and wherein said laser energy density and number oflaser pulses is sufficiently high that energy is deposited in saidphosphor layer and the entire thickness of at least a portion of saidphosphor layer is ablated.

[0015] In a preferred aspect, the thick film dielectricelectroluminescent display comprises, in sequence, a substrate, a lowerelectrode layer comprising an electrically conductive metallic film, athick film dielectric layer, a phosphor film layer deposited on thethick film dielectric layer, and an upper electrode layer comprising anoptically transparent electrically conductive film. In a preferredaspect, the phosphor film layer is an alkaline earth containing sulfideactivated with a rare earth metal. More preferred an europium activatedalkaline earth containing sulfide selected from the group consisting ofthioaluminates, thiooxyaluminates, thiogallates, thiooxygallates,thioindates, thiooxyindates and mixtures thereof.

[0016] According to yet another aspect of the invention, the methodfurther comprises selecting a laser pulse repetition rate that is lessthan about 100 kHz, preferably, in the range of about 10 Hz to 1 kHz.

[0017] According to still another aspect of the invention, the methodfurther comprises ablation of an optically transparent electricallyconductive film. In a preferred aspect, the optically transparentelectrically conductive film layer is an oxide, preferably, indium tinoxide.

[0018] According to still another aspect of the invention, the laserwavelength ranges of from about 193 nanometers to about 351 nanometers.In a preferred aspect, the laser is an excimer laser selected from thegroup consisting of krypton fluoride, xenon fluoride, xenon chloride,and argon fluoride excimer lasers.

[0019] According to yet another aspect of the invention, the thin filmphosphor layer comprises a material having an electronic band gap andthe laser wavelength is less than or equal to the wavelength thatcorresponds to the electronic band gap.

[0020] According to yet another aspect of the invention, the laserenergy density is dependent on specific heat and mass per unit area ofthe thin film phosphor layer. In a preferred aspect, the laser energydensity ranges from about 1 joule per square centimeter of surface areato about 2 joules per square centimeter of surface area and the laserpulse length is less than about 1 microsecond and preferably, at leastabout 20 nanoseconds.

[0021] According to yet another aspect of the invention, the thin filmphosphor layer has a thickness typically in the range of about 0.3 toabout 1 micrometer. In a preferred aspect, the laser ablation isconducted in an inert atmosphere, preferably, the inert atmosphere ismade up of gases selected from the group consisting of argon, helium,nitrogen and mixtures thereof.

[0022] According to yet another aspect of the invention, adjacent to thethin film phosphor layer is at least one protective layer. In apreferred aspect of the invention, the at least one protective layercomprises a material that allows laser radiation to pass through to thethin film phosphor layer and/or substantially reflects back anyradiation released by the thin film phosphor layer. In another preferredaspect, two protective layers are adjacent to the thin film phosphorlayer such that the thin film phosphor layer is encapsulated.

[0023] According to yet another aspect of the invention, the at leastone protective layer is a material selected from the group consisting ofoxides and sulfides. Preferably, the material is crystalline and morepreferably, selected from the group consisting of alumina, indium tinoxide, barium sulfide and mixtures thereof. In a preferred aspect of theinvention, the at least one protective layer comprises a crystallinematerial with an optical phonon frequency range that substantiallyreflects radiation in a wavelength range that substantially encompassesthe wavelength range of the radiation emitted from the thin filmphosphor layer during ablation. In another preferred aspect, the atleast one protective layer is substantially reflecting of a wavelengthof radiation at least in the range of from about 1 micrometers to about4 micrometers emitted from the thin film phosphor layer during ablation,more preferably in the range of from about 1.8 micrometers to about 3micrometers.

[0024] According to yet another aspect of the invention, there isprovided a thick film dielectric electroluminescent display comprising,in sequence, a substrate, a lower electrode layer comprising anelectrically conductive metallic film, a thick film dielectric layer, apatterned phosphor film layer patterned in accordance with the methoddescribed above, and an upper electrode layer comprising an opticallytransparent electrically conductive film.

[0025] In a preferred aspect, a thin film layer having a thickness lessthan 0.5 micrometers is between the thick dielectric layer and thephosphor film layer. Preferably, the thin film layer is barium titanate.In another preferred aspect, adjacent to the phosphor film layer is atleast one protective layer. Preferably, the at least one protectivelayer comprises a material that allows laser radiation to pass throughto the thin film phosphor layer and/or substantially reflects back anyradiation released by the thin film phosphor layer. More preferably, twoprotective layers are adjacent to the thin film phosphor layer such thatthe thin film phosphor layer is encapsulated. The at least oneprotective layer may be made from material with properties as describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will become more fully understood from thedescription given herein, and from the accompanying drawing, which isgiven by way of illustration only and does not limit the intended scopeof the invention.

[0027]FIG. 1 shows a section of a thick film dielectricelectroluminescent element display; and

[0028]FIG. 2 shows a section of a thick film dielectricelectroluminescent element display with patterned layers.

DETAILED DESCRIPTION OF THE INVENTION

[0029] As used herein, the term “pattern” refers to a design in a thinlayer. “Patterning” is the process of creating the design in a thinlayer. The term “in sequence” is defined as being in a particular orderbut this term is not to be limiting in the sense that, for instance, inthe case of layering to form a display, that the layers be adjacent toone another.

[0030] The present invention relates to a laser ablation method forpatterning thin film layers for thick film dielectric electroluminescentdisplays without substantial ablation of or damage to other layers. Atypical thick dielectric electroluminescent display 10 is shown inFIG. 1. The thick electroluminescent display 10 comprises a basicstructure of, in sequence, a substrate 12, an electrically conductivefilm layer to form the lower electrode 14, a thick dielectric film layer16, a phosphor film 18, and an optically transparent but electricallyconductive film 20 to form the upper electrode in the structure. Thesubstrate 12 is preferably a heat resistant substrate such as ceramic,glass ceramic composite, high temperature glass, ceramic coated metal,or any other rigid material that will withstand the processingtemperatures. The lower electrode 14 is preferably gold or silver. Thelower electrode is preferably deposited on the substrate prior todeposition of the thick dielectric structure. The thick dielectric filmlayer 16 is designed to provide high resistance against dielectricbreakdown when the display is operated at the voltage required toproduce the display luminescence. Typically, the thick dielectric filmlayer 16 comprises a sintered perovskite, piezoelectric or ferroelectricmaterial such as lead magnesium niobate-titanate (PMN-PT) with adielectric constant of several thousand and a thickness greater thanabout 10 micrometers to prevent dielectric breakdown. The phosphor film18 typically comprises a sulfide containing phosphor such as an alkalineearth containing sulfide, for instance, an alkaline earth containingsulfide activated with a rare earth metal, preferably, an europiumactivated alkaline earth containing sulfide selected from the groupconsisting of thioaluminates, thiooxyaluminates, thiogallates,thiooxygallates, thioindates, thiooxyindates and mixtures thereof. Theupper electrode 20 is a transparent electrically conductive layer,typically, an oxide such as indium tin oxide (ITO). Typically, anotherthin layer is placed between the thick dielectric film layer and thephosphor layer, as described in International Patent ApplicationPCT/CA00/00561, hereby incorporated by reference. Preferably this otherthin film layer has a thickness less than 0.5 micrometers and, morepreferably, this other thin film layer is barium titanate.

[0031] In embodiments, the laser ablation method relates to patterningthin film phosphor layers 18 without substantial ablation of or damageto any other layer. In related embodiments, the laser ablation method isdirected to patterning thin film phosphor layers 18 and transparentelectrically conductive layers 20 without substantial ablation of ordamage to any other layer (see FIG. 2).

[0032] In general, the method involves irradiating the layer to beablated above a temperature at which it can be vaporized while limitingthe transfer of heat energy to any other layer. This prevents, forinstance, the immediately adjacent thin film from melting, undergoingchemical reactions within itself, with the layer to be ablated, or anyother portion of the structure that may result in significantdegradation of the electroluminescent display.

[0033] In preferred embodiments, the method of laser ablation entailsthe selection of a wavelength of the laser radiation, a laser pulselength, a laser energy density and a sufficient number of laser pulsesdelivered to a specific area of the film to be ablated to obtain apatterned layer. These parameters are selected to be compatible with thephysical properties of the layer to be ablated and any other layer notto be ablated. These properties may include the optical absorptioncoefficient and optical index of refraction of the layer to be ablatedat the specific laser wavelength and any other layer not to be ablatedat the specific wavelength; the heat capacity of the layer to be ablatedand the heat capacity of any other layer not to be ablated; and thethermal conductivity of the layer to be ablated and the thermalconductivity of any other layer not to be ablated.

[0034] In one embodiment, the laser ablation method comprises a)selecting a laser wavelength such that the laser radiation issubstantially absorbed within the layer to be ablated and any radiationnot absorbed by this layer dissipates without substantial absorption byany other layer, for example, the radiation that is not absorbed isreflected from the interface between the layer to be ablated and anunderlying thin film; b) selecting a laser pulse length such that it issufficiently short that during the duration of a laser pulse there is nosubstantial heat flow from the layer to be ablated to any other layer,in particular, any underlying thin film; c) selecting a laser energydensity of the laser pulse such that it is sufficiently high that energyis deposited in the layer to vaporize the entire thickness of at least aportion of the layer; d) selecting a sufficient number of laser pulsesand a laser pulse repetition rate such that it is sufficiently high thatenergy is deposited in the layer to vaporize the entire thickness of atleast a portion of the layer. For instance, if the layer to be ablatedis only partially ablated using a single laser pulse, then a sequence ofpulses may be used to completely ablate the layer, if that is the user'schoice.

[0035] Preferably, the laser wavelength is less than or equal to thecorresponding electronic band gap of the material of the layer beingablated. The electronic band gap may be influenced by the presence ofimpurities, defects in the crystallinity structure of the material, andgrain boundaries in the material. For instance, the layer to be ablatedmay comprise more than one chemical compound or crystalline phase, andin this case, the band gap of the other constituent materials may needto be taken into account. Similarly, the radiation that is not absorbedand is reflected, for instance, from the interface between the layer tobe ablated and the underlying layer, may be affected by the presence ofimpurities, the grain structure and other morphological features of thematerials of the layers. The thermal conductivity of the layer to beablated and any other layer not to be ablated may also be influenced bythe grain structure and physical morphology of the other constituentmaterials of these layers. In preferred embodiments, laser wavelengthsfor ablation are in the range of from about 193 nanometers to about 351nanometers. To achieve this selected wavelength range, excimer lasersmay be used. More preferably, these lasers are selected from the groupconsisting of krypton fluoride, xenon fluoride, xenon chloride, andargon fluoride excimer lasers.

[0036] Preferably, the laser pulse length is at least about 20nanoseconds and, more preferably, less than about one microsecond suchthat there is no undue heating of any other layer underlying the layerto be ablated. The layer to be ablated has a thickness typically in therange of about 0.3 to about 1 micrometer.

[0037] Preferably, the laser energy density is dependent on specificheat and mass per unit area of the layer to be ablated. Typically, aenergy density of between about 1 joule per square centimeter of surfacearea and 2 joules per square centimeter of surface area are required forclean ablation. Excimer lasers can typically deliver a energy density inexcess of 3 joules per square centimeter.

[0038] Preferably, the pulse repetition rate is less that about 100 kHz.Most commercially produced excimer lasers typically have a pulserepetition rate in the range of about 10 Hz to 1 kHz. If the repetitionrate is too high, the heat from an incident laser pulse will not havedissipated into the layer before another pulse arrives, which may resultin possible overheating of the other layers, in particular, the layerunderlying the layer to be ablated.

[0039] In preferred embodiments, the laser ablation is conducted in anessentially inert atmosphere. Typically, the inert atmosphere is made upof gases selected from the group consisting of argon, helium, nitrogenand mixtures thereof.

[0040] To successfully ablate a layer, it is desirable to be able tocontrol the temperature distribution of the layer to be ablated toachieve a clean ablation of the material. For example, if the surface ofthe material solidifies while material below is molten or vaporized, thematerial may not be cleanly ablated, and portions of it may re-condenseor solidify. If this happens, the ablated region may have condensed andsolidified debris scattered randomly over it. In order to control thetemperature distribution of the layer to be ablated and to achieve aclean ablation of the material, a protective layer may be used. In oneembodiment, a protective layer may be deposited on top of the layer tobe ablated. The protective layer permits laser radiation to pass throughto the layer to be ablated and the protective layer substantiallyreflects back any radiation released by the layer being ablated.Similarly, a protective layer may be positioned below the layer to beablated so that any radiation released by the layer being ablated issubstantially reflected back. In addition, the layer to be ablated maybe encapsulated with a protective layer. For instance, the protectivelayer is positioned on top and below the layer to be ablated.Preferably, the combined thickness of the layer to be ablated and theprotective layer is in the range of about 0.3 to about 1.5 micrometers.

[0041] The protective layers are selected so that they are compatiblewith the electroluminescent display and the remainder of the displayprocessing steps following the ablation steps, since the protectivelayers remain in place after ablation. In embodiments incorporating theprotective layer, the method preferably entails the selection of achoice of materials and thickness for the protective layer, a wavelengthof the laser radiation, a laser pulse length, a laser energy density, apulse repetition rate and a total number of pulses delivered to aspecific area of the film to be ablated to achieve this result. Theprotective layer is typically a material that permits laser radiation topass through to the layer to be ablated and substantially reflects backany radiation released by the layer being ablated, preferably thematerial is a crystalline material. Typically, the protective layercomprises compounds containing light atoms such as oxides and/orsulfides, preferably having a relatively high degree of ionic bondingwithin the crystal lattice. More preferably, the protective layer isselected from the group consisting of alumina, indium tin oxide, bariumsulfide and mixtures thereof.

[0042] In preferred embodiments, the protective layer is a crystallinematerial having a wide range of optical phonon frequencies such that itis capable of substantially reflecting back the wavelength range ofradiation, in particular black body radiation, emitted by the layer tobe ablated as it approaches its vaporization temperature. The termoptical phonon is as defined in C. Kittel, Introduction to Solid StatePhysics Third edition; Chapter 5. In particular, the protective layercomprises a material with an optical phonon frequency range such that itsubstantially reflects radiation in a wavelength range thatsubstantially encompasses the wavelength range of the radiation, inparticular black body radiation, emitted from the ablated materialduring the ablation process. In particular embodiments, the protectivelayer is chosen to substantially reflect back to the phosphor layer ablack body radiation wavelength at least in the range of about 1micrometers to about 4 micrometers, preferably about 1.8 micrometers toabout 3 micrometers.

[0043] The protective layer can also protect the layer fromenvironmental degradation. For instance, the protective layer canprotect the unablated portion from the atmosphere and, thus, anymoisture therefrom.

[0044] In particular embodiments whereby the layer to be ablated is aphosphor, the vaporization temperature at which ablation occurs istypically in the range of about 1500° C. to about 2500° C. To avoidreduction of the vaporization temperature as radiation (ie. black bodyradiation) is released from the phosphor layer, a protective layer ischosen that will substantially reflect back to the phosphor layer theblack body radiation in the wavelength range emitted from the phosphorlayer. With respect to a phosphor with a vaporization temperaturetypically in the range of about 1500° C. to about 2500° C., thewavelength of the black body radiation emitted from the phosphor layerat these temperatures about is predominantly in the wavelength range ofabout 1.8 micrometers to about 3 micrometers, which is in the infraredregion of the electromagnetic spectrum. Therefore, the protective layeris chosen to substantially reflect back to the phosphor layer a blackbody radiation wavelength at least in the range of about 1.8 micrometersto about 3 micrometers.

[0045] The above disclosure generally describes the present invention. Amore complete understanding can be obtained by reference to thefollowing specific Examples. These Examples are described solely forpurposes of illustration and are not intended to limit the scope of theinvention. Changes in form and substitution of equivalents arecontemplated as circumstances may suggest or render expedient. Althoughspecific terms have been employed herein, such terms are intended in adescriptive sense and not for purposes of limitation.

EXAMPLES

[0046] The electroluminescent displays in the following examples werefabricated by depositing and patterning thin film layers on a 5centimeter by 5 centimeter alumina substrate upon which was deposited,in sequence, a thin film gold electrode and a composite thick filmdielectric layer, according to the methods of Applicant's co-pendingInternational Patent Application PCT/CA00/00561 (the entirety of whichis incorporated herein by reference). A barium titanate thin filmdielectric layer is then deposited thereon, according to the method ofApplicant's co-pending U.S. patent application Ser. No. 09/761,971 filedJan. 17, 2001 (the entirety of which is incorporated herein byreference). Following the deposition of the barium titanate film, aphosphor film layer was deposited thereon using the method ofApplicant's co-pending U.S. patent application Ser. No. 09/798,203 filedMar. 2, 2001, (the entirety of which is incorporated herein byreference). The phosphor layer comprises an europium activated magnesiumbarium thioaluminate with three atomic percent europium based on theratio of europium to magnesium and barium.

[0047] Ablation was achieved using an excimer laser focused onto thephosphor film layer of the display in a square spot of variabledimensions, in particular, 260 micrometers by 260 micrometers. The laserpulse length was 20 nanoseconds. The display was moved beneath the spotin a direction perpendicular to the laser beam so that the spot wasscanned across the phosphor layer at a rate of up to 300 centimeters perminute. The scanning rate was chosen so that sequential laser pulsesoverlapped so that repeated ablated spots formed an ablated trench.Several parallel trenches were ablated so that the phosphor film layerwas divided into parallel strips. The repetition rate was varied so thateach point in the ablated trench was subjected to at least two and up tofive laser pulses.

[0048] Following ablation of the phosphor film layer, an additional thinfilm layer of alumina was deposited thereon, followed by the depositionof a transparent electrode layer of indium tin oxide. It is possiblethat these layers may already be deposited prior to the ablationprocess, wherein the alumina acts as the protective layer to protect theablated layer and any other layers.

[0049] The resulting electroluminescent displays were then tested byapplying alternating polarity voltage pulses with an amplitude of 60volts above the threshold value, a pulse width of 32 microseconds and apulse repetition rate of 240 Hz.

Example 1

[0050] A thick film electroluminescent display was made as describedabove, wherein the europium activated magnesium barium thioaluminatephosphor film layer is about 270 nanometers thick and the underlyinglayer of barium titanate is about 15 nanometers thick. To the top of thephosphor film layer was sputtered a protective layer of alumina, whichis about 45 nanometers thick, followed by a layer of indium tin oxide,which is about 100 nanometers thick. The indium tin oxide acts as bothan electrode and protective layer for the display.

[0051] The phosphor film layer together with the overlying layers wereablated using an excimer laser having a laser wavelength of 248nanometers, a laser energy density of 1.5 joules per square centimeterand a laser pulse repetition rate to give a pulse every 26 micrometersalong the ablation path.

[0052] This resulted in a phosphor film layer that could beindependently illuminated by applying a voltage between the goldelectrode and the indium tin oxide layer. The luminosity of the phosphorwas measured and it was found that the unablated area was comparable tothat of an unpatterned but otherwise identical device.

Example 2

[0053] A display similar to that of Example 1 was fabricated, exceptthat the laser energy density was higher at 2 joules per squarecentimeter and the laser pulse repetition rate was lower so that therewas a pulse applied every 52 micrometers along the ablation trench.

[0054] This display performed similarly to that of Example 1.

[0055] Although preferred embodiments of the invention have beendescribed herein in detail, it will be understood by those skilled inthe art that variations may be made thereto without departing from thespirit of the invention.

We claim:
 1. A laser ablation method for patterning a thin film phosphorlayer of a thick film dielectric electroluminescent display, havingother layers, the method comprising selecting a wavelength of laserradiation, a laser pulse length, a laser energy density and a sufficientnumber of laser pulses to pattern the thin film phosphor layer withoutsubstantial ablation of or damage to other layers, whereby thewavelength of laser radiation is such that the laser radiation issubstantially absorbed by the thin film phosphor layer with minimalabsorption by other layers, the laser pulse length is sufficiently shortthat during the duration of the laser pulse there is minimal heat flowfrom the thin film phosphor layer to other layers, and the laser energydensity and the sufficient number of laser pulses is sufficiently highthat energy is deposited in the thin film phosphor layer, whereby theentire thickness of at least a portion of the thin film phosphor layeris ablated.
 2. A laser ablation method according to claim 1, wherein themethod further comprises selecting a laser pulse repetition rate lessthan about 100 kHz.
 3. A laser ablation method according to claim 1,wherein the method further comprises ablation of an opticallytransparent electrically conductive film.
 4. A laser ablation methodaccording to claim 1, wherein the phosphor film layer is an alkalineearth containing sulfide activated with a rare earth metal.
 5. A laserablation method according to claim 4, wherein the alkaline earthcontaining sulfide activated with a rare earth metal is a europiumactivated alkaline earth containing sulfide selected from the groupconsisting of thioaluminates, thiooxyaluminates, thiogallates,thiooxygallates, thioindates, thiooxyindates and mixtures thereof.
 6. Alaser ablation method according to claim 3, wherein the opticallytransparent electrically conductive film layer is an oxide.
 7. A laserablation method according to claim 6, wherein the optically transparentelectrically conductive film layer is indium tin oxide.
 8. A laserablation method according to claim 1, wherein the thin film phosphorlayer comprises a material having an electronic band gap and the laserwavelength is less than or equal to the wavelength that corresponds tothe electronic band gap.
 9. A laser ablation method according to claim8, wherein the laser wavelength ranges of from about 193 nanometers toabout 351 nanometers.
 10. A laser ablation method according to claim 9,wherein the laser is an excimer laser selected from the group consistingof krypton fluoride, xenon fluoride, xenon chloride, and argon fluorideexcimer lasers.
 11. A laser ablation method according to claim 1,wherein the laser energy density is dependent on specific heat and massper unit area of the thin film phosphor layer.
 12. A laser ablationmethod according to claim 11, wherein the laser energy density rangesfrom about 1 joule per square centimeter of surface area to about 2joules per square centimeter of surface area.
 13. A laser ablationmethod according to claim 2, wherein the laser pulse repetition rate isin the range of about 10 Hz to 1 kHz.
 14. A laser ablation methodaccording to claim 1, wherein the laser pulse length is less than about1 microsecond.
 15. A laser ablation method according to claim 14,wherein the laser pulse length is at least about 20 nanoseconds.
 16. Alaser ablation method according to claim 1, wherein the thin filmphosphor layer has a thickness typically in the range of about 0.3 toabout 1 micrometer.
 17. A laser ablation method according to claim 1,wherein the laser ablation is conducted in an inert atmosphere.
 18. Alaser ablation method according to claim 17, wherein the inertatmosphere is made up of gases selected from the group consisting ofargon, helium, nitrogen and mixtures thereof.
 19. A laser ablationmethod according to claim 1, wherein adjacent to the thin film phosphorlayer is at least one protective layer.
 20. A laser ablation methodaccording to claim 19, wherein the at least one protective layercomprises a material that allows laser radiation to pass through to thethin film phosphor layer.
 21. A laser ablation method according to claim19, wherein the at least one protective layer comprises a material thatsubstantially reflects back any radiation released by the thin filmphosphor layer.
 22. A laser ablation method according to claim 20,wherein the at least one protective layer comprises a material thatsubstantially reflects back any radiation released by the thin filmphosphor layer.
 23. A laser ablation method according to claim 19,wherein two protective layers are adjacent to the thin film phosphorlayer such that the thin film phosphor layer is encapsulated.
 24. Alaser ablation method according to claim 19, wherein the at least oneprotective layer comprises a material selected from the group consistingof oxides and sulfides.
 25. A laser ablation method according to claim24, wherein the material is crystalline.
 26. A laser ablation methodaccording to claim 25, wherein the crystalline material is selected fromthe group consisting of alumina, indium tin oxide, barium sulfide andmixtures thereof.
 27. A laser ablation method according to claim 19,wherein the at least one protective layer comprises a crystallinematerial with an optical phonon frequency range that substantiallyreflects radiation in a wavelength range that substantially encompassesthe wavelength range of the radiation emitted from the thin filmphosphor layer during ablation.
 28. A laser ablation method according toclaim 19, wherein the at least one protective layer is substantiallyreflecting of a wavelength of radiation at least in the range of fromabout 1 micrometers to about 4 micrometers emitted from the thin filmphosphor layer during ablation.
 29. A laser ablation method according toclaim 19, wherein the at least one protective layer is substantiallyreflecting of a wavelength of radiation at least in the range of fromabout 1.8 micrometers to about 3 micrometers emitted from the thin filmphosphor layer during ablation.
 30. A thick film dielectricelectroluminescent display comprising, in sequence, a substrate; a lowerelectrode layer comprising an electrically conductive metallic film; athick film dielectric layer; a patterned phosphor film layer patternedin accordance with the method of claim 1; and an upper electrode layercomprising an optically transparent electrically conductive film.
 31. Athick film dielectric electroluminescent display comprising, insequence, a substrate; a lower electrode layer comprising anelectrically conductive metallic film; a thick film dielectric layer; apatterned phosphor film layer patterned in accordance with the method ofclaim 2; and an upper electrode layer comprising an opticallytransparent electrically conductive film.
 32. A thick film dielectricelectroluminescent display according to claim 30, wherein the phosphorfilm layer is an alkaline earth containing sulfide activated with a rareearth metal.
 33. A thick film dielectric electroluminescent displayaccording to claim 32, wherein the alkaline earth containing sulfideactivated with a rare earth metal is a europium activated alkaline earthcontaining sulfide selected from the group consisting of thioaluminates,thiooxyaluminates, thiogallates, thiooxygallates, thioindates,thiooxyindates and mixtures thereof.
 34. A thick film dielectricelectroluminescent display according to claim 30, wherein the laserwavelength ranges of from about 193 nanometers to about 351 nanometers.35. A thick film dielectric electroluminescent display according toclaim 34, wherein the laser is an excimer laser selected from the groupconsisting of krypton fluoride, xenon fluoride, xenon chloride, andargon fluoride excimer lasers.
 36. A thick film dielectricelectroluminescent display according to claim 30, wherein the laserenergy density is dependent on specific heat and mass per unit area ofthe phosphor film layer.
 37. A thick film dielectric electroluminescentdisplay according to claim 36, wherein the laser energy density rangesfrom about 1 joule per square centimeter of surface area to about 2joules per square centimeter of surface area.
 38. A thick filmdielectric electroluminescent display according to claim 30, wherein thelaser pulse length is less than about 1 microsecond.
 39. A thick filmdielectric electroluminescent display according to claim 30, wherein thephosphor film layer has a thickness typically in the range of about 0.3to about 1 micrometer.
 40. A thick film dielectric electroluminescentdisplay according to claim 30, wherein a thin film layer having athickness less than 0.5 micrometers is between the thick dielectriclayer and the phosphor film layer.
 41. A thick film dielectricelectroluminescent display according to claim 40, wherein the thin filmlayer is barium titanate.
 42. A thick film dielectric electroluminescentdisplay according to claim 30, wherein adjacent to the phosphor filmlayer is at least one protective layer.
 43. A thick film dielectricelectroluminescent display according to claim 42, wherein the at leastone protective layer comprises a material that allows laser radiation topass through to the phosphor film layer.
 44. A thick film dielectricelectroluminescent display according to claim 42, wherein the at leastone protective layer comprises a material that substantially reflectsback any radiation released by the phosphor film layer.
 45. A thick filmdielectric electroluminescent display according to claim 43, wherein theat least one protective layer comprises a material that substantiallyreflects back any radiation released by the phosphor film layer.
 46. Athick film dielectric electroluminescent display according to claim 42,wherein two protective layers are adjacent to the phosphor film layersuch that the phosphor film layer is encapsulated.
 47. A thick filmdielectric electroluminescent display according to claim 42, wherein theat least one protective layer comprises a material selected from thegroup consisting of oxides and sulfides.
 48. A thick film dielectricelectroluminescent display according to claim 47, wherein the materialis crystalline.
 49. A thick film dielectric electroluminescent displayaccording to claim 48, wherein the crystalline material is selected fromthe group consisting of alumina, indium tin oxide, barium sulfide andmixtures thereof.
 50. A thick film dielectric electroluminescent displayaccording to claim 42, wherein the at least one protective layercomprises a crystalline material with an optical phonon frequency rangethat substantially reflects radiation in a wavelength range thatsubstantially encompasses the wavelength range of the radiation emittedfrom the phosphor film layer during ablation.
 51. A thick filmdielectric electroluminescent display according to claim 42, wherein theat least one protective layer is substantially reflecting of awavelength of radiation at least in the range of from about 1micrometers to about 4 micrometers emitted from the phosphor film layerduring ablation.
 52. A laser ablation method according to claim 42,wherein the at least one protective layer is substantially reflecting ofa wavelength of radiation at least in the range of from about 1.8micrometers to about 3 micrometers emitted from the phosphor film layerduring ablation.
 53. A laser ablation method for patterning a rare earthactivated alkaline earth sulfide phosphor film layer within a thick filmdielectric electroluminescent display comprising other layers, themethod comprising: providing a wavelength of laser radiation, a laserpulse length, a laser energy density and a sufficient number of laserpulses to said phosphor layer to effect patterning of said phosphorlayer without substantial ablation of, or damage to other layers,wherein said wavelength is substantially absorbed by said phosphor layerand there is minimal heat flow from said phosphor layer to other layers,and wherein said laser energy density and number of laser pulses issufficiently high that energy is deposited in said phosphor layer andthe entire thickness of at least a portion of said phosphor layer isablated.
 54. The method of claim 53, wherein said laser wavelength isabout 193 nm-351 nm, said laser pulse length is at least about 20nanoseconds, said laser energy density is about 1-2 joules per cm² andsaid pulse repetition rate is less than about 100 kHz.
 55. The method ofclaim 54, wherein about 0.3 to 1.0 micrometers of said phosphor layer isablated.
 56. The method of claim 53, wherein said method is conducted inan inert atmosphere of gases.